Heating and ventilating systems of this type are being used in motor vehicles, particularly passenger cars, to prevent fogging and icing of vehicle windshields and windows. They also serve to supply the vehicle occupant compartment with fresh air of the desired temperature. The desired temperature does not only depend on the season of the year, but is also very much related to the particular comfort requirements of the individual. However, as a general rule, it is desirable that the air supplied into the leg room be of a higher temperature than the air supplied to the upper region of the vehicle compartment, i.e. the dashboard area.
The aforementioned comfort considerations in regard to heating and ventilating the vehicle occupant compartment require that the admitted air be regulated in a variety of ways in terms of air flow rate and temperature.
The use of controllable valves or doors for raising the temperature of the cold air drawn in by the blower fan is known in the art. According to the state of the art, such valves or doors are usually controlled by mechanical, electrical or pneumatic means. However, controls of this type usually require the use of complex motion transmitting devices, such as Bowden wires, rods, linkages, servomotors, vacuum units or the like.